well,the way i see it,just because psp has superb graphic possibilities,doesn't mean that every game has to be in 3d.i'm sure 2d games will be made as well,and some are already in the lineup,like rpgs and puzzle games,or fighting games .it only means that if they want 2d graphics,it will be kick ass 2d,and if they want 3d graphics,it will still be kick ass 3d.
take lumines,is that a super 3d game?no,it's 2d puzzle game.
on the other hand,i can already see everyone trying really hard to implement some sort of touch screen functionality in their ds games,but it's like they're forced to.
to be really innovative,a ds game has to be conceived with really interesting touch screen concepts from the start,and have lots of them,otherwise it's just another handheld game with some extra.
so,at that point,why go for the ds when you can make an overall better game on psp.it doesn't have to be ps2 like graphics,but it can do that.i think it's more interesting.ds now has to have 3d games,if they wanted 2d graphics the gba could do those well enough.